Forming a bag from a tubular material by folding at least one cross bottom is a conventional method. In this case, a cross bottom may be provided on both ends of the bag tube, in particular a valve also being insertable into one of the cross bottoms, so that a valve bag capable of being filled by a bag filling machine via a filling connection piece is formed. However, it is also possible, for example, to form a bag bottom on only one side of the tube and to fill the bag open at the top and after filling to close it, for example by stitching, gluing, closing by means of adhesive or touch-and-close fastening strips etc.
A filled bag should be closed so as to be as leaktight as possible, in order, where dusty materials are concerned, to prevent dust from escaping from the material. When the filled bag has been transported to a destination where the introduced product is to be used, the bag is torn open so that the introduced material can be poured out or otherwise extracted. Since the bag bottom consists of numerous plies which have been glued to one another, the bag bottom is not appropriate for the tearing-open operation. Tearing open the bag underneath the bottom takes place in the tubular material of the casing wall of the bag. If tearing open is carried out freely, it often happens that the tear made does not run transversely with respect to the longitudinal axis of the bag in the desired way, but, instead, occurs obliquely with a component in the axial direction. In this case, it may happen that the tear continues, level with the product introduced in the bag, so that, even when the bag is being torn open, an undesirable escape of product from the bag occurs and the area where the bag is torn open is contaminated. One remedy may be to open the bag by means of a sharp cutting instrument in the form of a scissor or a knife. This has the disadvantage of the resulting time required for opening the bag and the fact that an extra aid provided, which has to be kept operational, is always needed for opening the bag.